<!DOCTYPE html>
<html>
<head>
  <meta charset="UTF-8" />
  <title>title</title>
</head>
<style>
.flex-container {
  display: flex;
  flex-direction: row;
  flex-wrap: wrap;
  text-align: center;
}
.header {
  
}
.header {background: coral;}
.footer {background: lightgreen;}
.aside1 {background: moccasin;}
.aside2 {background: violet;}

.flex-container > * {
    padding: 10px;
    flex: 1 100%;
}
@media screen and (min-width: 500px) {
  .aside {
    flex:3 auto;
  }
}
@media all and (min-width: 800px) {
    .main    { flex: 3 0px; }
    .aside1 { order: 1; } 
    .main    { order: 2; }
    .aside2 { order: 3; }
    .footer  { order: 4; }

</style>
<body>
  <div class="flex-container">
    <header class="header">头部</header>
    <article class="main">
      <p>菜鸟教程 - 学的不仅是技术，更是梦想！菜鸟教程(www.runoob.com)提供了最全的编程技术基础教程, 介绍了HTML、CSS、Javascript、Python，Java，Ruby，C，PHP , MySQL等各种编程语言的基础知识。 同时本站中也提供了大量的在线实例，通过实例，您可以更好的学习编程。</p>
    </article>
    <aside class="aside aside1">边栏 1</aside>
    <aside class="aside aside2">边栏 2</aside>
    <footer class="footer">底部</footer>
  </div>
</html>